Something to keep in mind, it because girls mature faster than males, it isn't until around 14-15 years old that boys outpace girls in muscle development and growth spurts on average. It's not universal, but around 12-13 it's normal for girls the same age as boys to be taller and/or stronger (not by leaps and bounds, but measurably enough to make a difference).
After that... it rapidly - and I do mean RAPIDLY - changes in the boys favor.
Combine teenage boy hormones (and, hey, girls experience that shit too) with them also getting stronger and there's a reason why things get awkward even for tomboys around that age.